PHNX Materials, a California-based cleantech startup, has devised a method for extracting valuable compounds from fly ash — a finely divided toxic byproduct created from the combustion of pulverized coal — to make it appropriate for use in the manufacture of concrete.

With the aim of reducing the emissions associated with the production of cement, which is the binding agent in concrete, and decarbonizing the concrete industry (wherein the production of one kilogram of cement releases about one kilogram of CO₂), the new process promises to significantly reduce the carbon footprint of cement, which is reportedly responsible for about 8% of global CO₂ emissions.

Source: ATS

The researchers explained that while significant amounts of fly ash do exist, it tends to be too contaminated for use in concrete without treatment. As such, the team suggests that treated ash could potentially replace up to 30% of cement.

Because cement emits large amounts of CO₂ — both from the high-temperature kilns used in its production and from the chemical reaction that creates it — the researchers suggest that displacing cement with processed fly ash can produce more sustainable concrete without impacting performance.

To accomplish this, the company’s approach focuses on sulfur and carbon, which are the common impurities in fly ash that concrete makers typically reject. By removing these contaminants, the ash is not only purified for construction use, the process also produces marketable byproducts like sulfur for use in fertilizer and aluminum for use in manufacturing, for instance.

“Unlocking this hidden supply is the fastest and most scalable way to decarbonize concrete,” the researchers concluded.